The present invention relates to a device for testing cans and to a method for measuring the internal pressurization of cans.
Uniformly retorting containers of food in an industrial canning process has posed formidable problems of quality control. The formidable problems have included identifying a small number of cans that are either underpressurized or overpressurized after being retorted, before the cans are opened by an end user. Cans that are under too much pressure following a retorting step are dangerous for an end user because the cans may explode. At the very least, cans under excessive pressure are extremely inconvenient to use because when the cans are opened, food is likely to be propelled out of the cans.
Cans may also be underpressurized because an improperly formulated mixture is placed in a particular can or because the can has not been adequately retorted. An improperly formulated mixture is unacceptable to an end user because it is not what the user expected. Additionally, a can that has not been sufficiently retorted poses a health hazard because the can has not been subjected to conditions that kill pathogenic microbes.
It is desirable then for an industrial canner to have a method of testing a suitable number of cans to determine whether the retorting process has been satisfactorily performed. One testing method has included a use of cans having a series of ridges and valleys pressed into the cans and extending radially around the cans. The ridges and valleys are formed on the can in order to provide the can with a mechanism for stretching or for being compressed.
Once a group of cans has been filled with food and retorted, a statistically significant number of cans are selected for testing. The distance between the crown of a ridge and a base of the valley on each can is measured with a hand held instrument that measures length. Manually measuring cans by this method has been unsatisfactory because the method is not standardized. In the manual measurement of can length, a human tester manually employs the measuring instrument, touching it to the can with one hand while holding the can in another hand. If the tester does not have extremely steady hands or cannot draw a completely straight line along the ridges and valleys of the can, or cannot center the measuring instrument with respect to the axial center of the can, the results will be inaccurate. Also, because each tester has his or her own style of performing the test, comparing results among testers is not practical.